Fuel injectors (a.k.a. fuel nozzles) are important components of gas turbines as well as other gas combustion engines. Because the fuel nozzle is the source of the fuel, the fuel nozzle can provide significant play in the role of engine performance.
Because the fuel nozzle extends into the combustion chamber (a.k.a. the combustor), typically, a fuel nozzle includes an external support/stem through which an internal fuel tube extends. The fuel tube will be connected to an atomizer or other tip to improve the delivery state of the fuel so that it will properly mix with air in the combustion chamber.
During operation, and particularly within a turbine engine, the support/stem is surrounded by high-temperature and high-pressure air exiting the compressor. However, it is desirable to deliver the fuel at a much lower temperature than the compressor air. More particularly, if too much heat is transferred to the fuel, the fuel can begin to coke, thereby ruining or reducing the quality of the fuel. Additionally, coke deposits can form on or in the fuel injector decreasing and in some instances entirely stopping flow through the fuel injector. Thus, there have been many attempts to reduce the amount of heat that can be transferred from the high-temperature compressor air to fuel passing through the fuel injector.
Unfortunately, the support/stem is typically a solid cast, wrought, forged, machined or similarly formed piece free of thermal barriers that can allow for significant heat transfer. Further, as the support/stem is exposed to the high-temperature compressor air, the support/stem experiences significant thermal stresses due to thermal expansion and contraction. The thermal stresses can be amplified by the temperature gradient between the high-temperature compressor air within the compressor discharger and the “colder” fuel passing through the fuel injector. As the support/stem is a solid piece, the material of the support/stem is exposed to internal interrelational stresses that can fatigue the support/stem, thereby weakening the structural strength of the fuel nozzle.
Further, a typical support/stem can have a low stiffness-to-mass ratio which promotes lower modal frequencies because of the solid configuration. Additionally, the fuel nozzle is typically mounted within a combustion chamber in a cantilevered configuration with a large atomizer tip at the end of the cantilever. This arrangement is much like a pendulum. This large mass at the end of the support/stem further promotes lower modal frequencies.
Finally, because the support/stem is typically a solid cast, wrought, forged, machined or similarly manufactured component, the manufacturing costs associated therewith can be significant. Particularly, if minor modifications to the fuel nozzle, and particularly the support/stem, are desired, new tooling and dies are often required which is costly, if not prohibitive.
The present invention relates to improvements over the current state of the art in fuel nozzles.